None.
Not Applicable.
This invention relates to wheel balancers and in particular to an improved wheel balancer including a wheel rim measurement device configured to map the inner surface of a wheel rim, a wheel rim rotational positioning device, and a correction weight placement indicator, each operating in conjunction to facilitate the proper placement of wheel imbalance correction weights on the wheel rim.
When balancing a vehicle wheel, several potential sources for operator error exist. First, there is a need to identify the proper correction planes on the wheel rim into which correction weights are to be placed. Second, the wheel rim must be correctly rotated to, and held in, a rotational position such that the operator can place an imbalance correction weight in the identified correction plane, and third, the operator must manually apply the imbalance correction weight to the wheel rim in the identified correction plane and at the proper rotational position.
As disclosed in WO Patent No. 97/28431 to Hunter Engineering Company for xe2x80x9cWheel Balancer With Servo Motorxe2x80x9d, herein incorporated by reference, the determination of unbalance in vehicle wheels is carried out by an analysis with reference to phase and amplitude of the mechanical vibrations caused by rotating unbalanced masses in the wheel. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. Each signal is the combination of fundamental oscillations caused by imbalance and noise.
It is well known in the art that a variety of types of imbalance correction weights are available for placing on the wheel to correct the measured imbalance. For example, adhesive-backed weights, patch balance weights and hammer-on weights are available from a number of different manufacturers. Most balancers assume that the wheel rim/tire assembly will be rotated to a particular rotational position (for example, disposing the desired weight correction position at the top (twelve o""clock) or bottom (six o""clock) rotational positions) for weight placement. This is generally not a problem, unless it would be more convenient to apply the weight with the wheel/tire assembly in a different orientation, for example, the four-five o""clock rotational position when the operator is standing facing the surface of the wheel mounted on the wheel balancer.
As described in the WO 97/28431 patent, drive systems for currently available balancers may be improved to aid in weight placement by automatically rotating and holding the wheel rim to the correct rotational position. Prior art balancers typically require the operator to manually rotate the wheel/tire assembly to the desired position for weight placement. These prior art balancers then use a manual brake or the application of rectified AC current to an AC induction motor to temporarily hold the shaft in the desired position. Manual rotation to the desired position is less than satisfactory since it requires the operator to interpret the balancer display correctly. Moreover, manual rotation itself is not desirable, since it ties up the operator""s time and attention. In conventional systems, the balancer motor cannot be used to rotate the wheel/tire assembly to the correct position since available motor controllers used in balancers are incapable of performing this function.
Using the motor itself to provide a braking action is not completely satisfactory either. Such braking is normally accomplished by applying rectified alternating current to an AC motor. This method is inherently subject to error. The actual stopping position may be incorrect if the tire is larger than average or turning too fast for the xe2x80x9cbrakexe2x80x9d to respond. Moreover, although currently available motor braking systems stop the wheel in approximately the correct position, they do not actual hold the tire in position since the motor would heat up if the xe2x80x9cbrakexe2x80x9d was left on. With conventional equipment, a wheel rim/tire assembly with sufficient static imbalance to overcome its own inertia, therefore, can roll away from the braked dynamic weight attachment position as soon as the braking energy is released.
Similarly, currently available balancers require that the wheel rim/tire assembly be manually rotated in practically all circumstances since those balancers have no capability for applying anything other than full power to the balancer motor. That is, the motor in conventional balancers is useful for accelerating the wheel/tire assembly to full speed for determining wheel imbalance, but not for accurately positioning the wheel/tire assembly subsequently for correction of that imbalance.
Accordingly, WO Patent No. 97/28431 discloses a wheel balancer including a shaft adapted for receiving a wheel/tire assembly, having a longitudinal axis and which is rotatable about the axis by a direct current motor so as to rotate a wheel/tire assembly removably mounted thereon. A rotation sensor assembly is provided for measuring rotation of the shaft about its longitudinal axis and a vibration sensor assembly is operatively connected to the shaft for measuring vibrations resulting from imbalance in the wheel rim/tire assembly. A control circuit controls the application of direct current to the direct current motor and determines from vibrations measured by the vibration sensor assembly at least one weight placement position on the wheel/tire assembly to correct the vibrations. The control circuit is responsive to determination of a weight placement position to controllably rotate the wheel rim/tire assembly to bring the weight placement position to a predetermined rotational location and to actively hold the wheel/tire assembly in that location. However, it remains up to the operator to correctly position the correction weight on the wheel rim surface.
To compensate for a combination of static imbalance (where the heaviest part of the assembly will seek a position directly below the mounting shaft) and couple imbalance (where the assembly upon rotation causes torsional vibrations on the mounting shaft), at least two correction weights are required which are separated axially along the wheel surface, coincident with weight location or imbalance correction xe2x80x9cplanesxe2x80x9d. For using clip-on weights the xe2x80x9cleft planexe2x80x9d comprises the left (innermost) rim lip circumference while the xe2x80x9cright planexe2x80x9d comprises the right rim lip. If adhesive weights are used, the planes can reside anywhere between the rim lips, barring physical obstruction such as wheel spokes, welds, and regions of excessive curvature.
With the wheel rim/tire assembly mounted to the balancer, the relative distances from a reference plane (usually the surface of the wheel mounting hub) to the planes are conventionally made known either by manually measuring with pull-out gauges and calipers and then entering the observed values through a keypad, potentiometer, or digital encoder, or by using an automatic electronic measuring apparatus. The radius at which the weights will be placed must also be entered, again either manually or by use of the electronic measuring apparatus. Conventional wheel balancers employ a computer configured to utilize this input weight plane information, together with variable weight amounts and variable radial placements, to identify the proper locations for the imbalance correction weights on the wheel rim. While utilization of such a system facilitates the placement of an imbalance correction weight by placing the vehicle wheel in a preferred, or optimal rotational position for weight placement, it does not reduce other sources of operator error, such as the placement of an imbalance weight in the incorrect balance plane, a poor selection of imbalance planes by the operator, or failure to compensate for the width of the installed imbalance weights.
U.S. Pat. No. 5,915,274 to Douglas for xe2x80x9cMethod of Correcting Imbalance on a Motor Vehicle Wheel,xe2x80x9d herein incorporated by reference, overcomes some of the problems associated with correctly determining the weight location xe2x80x9cplanesxe2x80x9d by providing an apparatus for mapping the surface of the wheel rim. The rim measuring apparatus scans and stores the contour of the surface of the wheel rim, allowing the balancer computer to identify optimal imbalance correction weight planes, and to present the operator with the best imbalance correction weight arrangement. The computer has effectively an infinite number of imbalance correction planes in which to place the correction weights, rather than only the two planes previously selected by the operator. The best plane locations, amount of weight, and even the number of weights, are calculated to result in a minimized residual static and dynamic imbalance while still using incrementally sized weights. A display on the balancer is used to show the actual scanned contour of the wheel, as well as the relative locations of the weights on the display wheel rim, enhancing user understanding and providing confidence that the measuring apparatus is working correctly. However, actual placement of the imbalance correction weights in the identified optimal balance correction planes, and at the ideal rotational positions, must still be done manually by an operator, guided by instructions displayed on the wheel balancer, or by a mechanical or electronic arm.
Finally, an improvement to conventional wheel balancers to aid in the actual placement of imbalance correction weights onto the wheel rim is disclosed in WO Patent No. 98/10261 to Snap-on Equipment Europe Limited for xe2x80x9cA Wheel Balancerxe2x80x9d, herein incorporated by reference. Specifically, the WO 98/10261 patent discloses a conventional wheel balancer having an AC drive motor, which requires the operator to input two imbalance correction planes manually, and which includes a laser light source for illuminating a spot of laser light on the wheel rim, in each of the imbalance correction planes identified by the operator, at the specific angular location for placement of the respective imbalance correction weights. The laser light dot formed on the inner surface of the wheel rim indicates the angular center line of the balance weight position, and an inner edge of the balance weight position, thereby indicating to the operator the precise position at which the imbalance correction weight is to be secured to the wheel rim. The disclosed system assumes that each imbalance correction weight is of a predetermined average width. Furthermore, the laser light dot is only displayed when the operator manually rotates the wheel rim/tire assembly such that the weight application point coincides with a predetermined weight application rotational position, such as the four o""clock position. If the wheel rim/tire assembly is rotated away from the predetermined weight application rotational position, either by the operator or by it""s own weight, the projected laser spot is turned off, preventing misplacement of the weight by the operator. However, since the rotation of the wheel rim/tire assembly to the predetermined weight application position is performed manually, it is difficult for an operator to maintain the wheel in the predetermined rotational position such that the laser light spot remains on while the correction weight is being applied, or the location is being cleaned of debris. Any slight movement of the wheel rim/tire assembly away from the predetermined rotation position results in the laser light spot being turned off, with no indication on the wheel to the operator in which direction the wheel must be rotated to restore the laser projected spot.
Accordingly, there is a need in the industry for a vehicle wheel balancer which facilitates the placement of imbalance correction weights to a wheel rim/tire assembly by eliminating or reducing the sources of operator error induced by the selection of correction weight balance planes, rotational positioning of the wheel rim/tire assembly for the application of the imbalance correction weights, and during the actual attachment of the imbalance correction weight to the wheel rim/tire assembly, through automation and improved operator guidance.
Briefly stated, the improved wheel balancer of the present invention includes a shaft adapted for receiving a wheel rim/tire assembly, a rotation sensor assembly for measuring rotation of the shaft about its longitudinal axis, and a motor operatively connected to the shaft for rotating the shaft about its longitudinal axis, thereby rotating the wheel rim/tire assembly. A control circuit controls the application of current to the motor to rotate the wheel rim/tire assembly at desired speeds and to actively hold the wheel rim/tire assembly at desired rotational positions. An automatic measuring apparatus is configured to scan the inner surface of the wheel rim/tire assembly to provide the balancer computer with contour information necessary to identify optimal correction weight plane optimum locations as well to present the operator with the best imbalance correction weight arrangement. The best plane locations, amount of correction weight, the number of correction weights, and the positions of the correction weights in the plane locations, are calculated by the balancer computer to result in a minimized residual static and dynamic imbalance while still using incrementally sized weights. Once the correction planes and rotational positions of the imbalance correction weights is identified, the balancer computer utilizes the motor drive to automatically index and hold the wheel rim/tire assembly at the proper rotational position for placement of the first imbalance correction weight, enhancing weight placement accuracy. To further enhance weight placement accuracy, a laser pointer assembly projects a laser dot onto the inner surface of the wheel rim/tire assembly at the axial position of the weight imbalance correction plane at which the imbalance correction weight is to be applied. The wheel rim/tire assembly is rotated automatically by the drive motor to each determined rotational position for application of successive correction imbalance weights, and the laser dot is correspondingly projected onto each imbalance correction plane in succession.
It is a further improvement over the prior art in that the wheel balancer of the present invention that the balancer computer is configured to permit placement of imbalance correction weights adjacent the outer lip of the wheel rim/tire assembly, and that the laser pointer assembly is configured to project a laser spot between spokes of the wheel rim/tire assembly to illuminate the proper spot for placement of such imbalance correction weights.
It is a further improvement over the prior art in that the wheel balancer of the present invention is configured to receive as input, the width of a variety of brands of imbalance correction weights, and to utilizes such input widths to adjust the identification of the placement location of individual imbalance correction weights on the wheel rim/tire assembly to provide for optimal imbalance correction, and to indicate the adjusted position using the laser pointer.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.